The long-term objective of this research is to establish ultrasound as a safe, effective, and non-invasive method for assessing fracture risk, an important component in clinical management of osteoporosis. Osteoporosis afflicts over 20 million people in the U.S., responsible for more than 275,000 hip fractures annually. Currently, the primary means for assessment relies on densitometric techniques. These methods subject the patient to ionizing radiation, are relatively expensive, and do not always provide good estimates of bone strength. Ultrasound offers several potential advantages. It is non-ionizing and relatively inexpensive. Moreover, since ultrasound is a mechanical wave and interacts with bone in a fundamentally different manner than electromagnetic radiation, it may be able to provide more accurate estimates of bone strength compared with current densitometric methods. The goal of this research is to significantly improve the effectiveness of current ultrasonic bone assessment techniques by demonstrating the feasibility of a new approach to ultrasonic bone assessment. The approach entails the use of phased array source and receivers to reproducibly measure the finger bones (phalanges). In addition, the method utilizes multidirectional measurements to characterize both the trabecular (distal and proximal) and cortical (diaphyseal) portions. The specific aims are (i) to use 3D ultrasound simulations to demonstrate that phased array source and receiver measurements can reproducibly estimate a set of ultrasound parameters associated with phalangeal bones; and (ii) that combining data obtained from two directions can provide additional information on bone density and structure. The results of this study should allow development of a clinical prototype for non-invasive assessment of bone strength and fracture risk.